This process will take six months, and employs a technique known as aerobraking, whereby the spacecraft slows itself down by using the friction created each time it brushes past the Martian atmosphere.

The orbiter will have to perform this technique more than 500 times and each manoeuvre is perilous, as Professor Colin Pillinger, who led the UK's failed Beagle 2 mission to Mars in 2003, observed:

"If it goes in [the planet's atmosphere] too far it heats up and crashes and burns. If it hits the atmosphere at the wrong speed, it bounces off and goes off into deep space."

Detailed photos

In November 2006, once the orbiter is in the optimal position, the two-year science phase of the mission will commence.

The spacecraft carries a pay-load of six scientific instruments and is equipped with cameras capable of taking close-up images of the planet's surface.

"Previous orbiters could see something the size of a double-decker bus on the surface of Mars - this can see a dinner table," said Dr Matthew Genge, of Imperial College, London.

"So that means we can see things like a small spring of hot water coming out of the ground, if such a thing exists."

The Nasa mission team says that MRO will return 10-times more data than all of the previous Mars missions put together.

It will build up a detailed picture of how Mars has changed over the millennia: whether there were once rivers or oceans and what its climate was like during the geological past.

"The missions currently at Mars have each advanced what we know about the presence and history of water on Mars, and one of the main goals for Mars Reconnaissance Orbiter is to decipher when water was on the surface and where it is now," said JPL's Dr Richard Zurek, project scientist for the mission.

"Water is essential for life, so that will help focus future studies of whether Mars has ever supported life."

The spacecraft will also locate landing sites for future Martian missions.